Geochemical exploration method

ABSTRACT

The method of exploring for deposits of bittern salts such as sylvinite and carnallite which comprises collecting samples of formation, aqueous fluids and determining the concentrations of calcium, magnesium, or potassium and one or more of bromine and rubidium in said fluids. Parameter indicators include the individual concentrations of bromine and rubidium and the concentration ratios of bromine to potassium, (magnesium plus calcium) to rubidium and (magnesium plus calcium) to bromine. Regressional correlations of these parameters indicate plan and profile directions to the desired salts.

l 7 5 5 O o S R O+-U4-72 XR 396539837 i 0 United States Patent [151 3,653,837 Egleson [4 1 Apr. 4, 1972 54] GEOCHEMICAL EXPLORATION OTHER PUBLICATIONS METHOD l-lackh s Chemical Dictionary, Grant, ed., 4th ed. p. 101, Me- [72] Inventor: Granville C. Egleson, Houston, Tex. 1965 [73] Assignee: The Dow Chemical Company, Midland, primary Emmine,. Morris O w Mlch- Assistant Examiner-R. E. Serwin Mar Attorney-Griswold & Norris and S. Jowanovitz [21] App1.No.: 20,139

[57] ABSTRACT [52] U.S. Cl. .Q ..23/230 EP, 175/50 The method of exploring for deposits of bittern salts such as [51] Int. Cl ..G01m 15/00, G0lm 33/18, (30111 33/24 sylvinite and carnallite which comprises collecting samples of 58 Field or Search .(23/230, 253; 175/50; 73/61.1. formation, aqueous fluids and determining the concentrations of calcium, magnesium, or potassium and one or more of [56] References Cited bromine and rubidium in said fluids. Parameter indicators include the individual concentrations of bromine and rubidium UNITED STATES PATENTS and the concentration ratios of bromine to potassium, (magnesium plus calcium) to rubidium and (magnesium plus calci- 2,367,592 1/ 1945 McDermott ..23/230 um) to bmmine Regression] correlations of these parame 2'37O'793 3/1945 P- 23/230 ters indicate plan and profile directions to the desired salts. 2,374,937 5/1945 Horv1tz..... 23/230 2,551,449 5/1951 Menke ..23/230 X 7 Claims, No Drawings Jim-w n. 5',- "r t". \i

GEOCIIEMICAL EXPLORATION METHOD 7 This invention relates to a method of geochemical prospecting for hidden bittem salt deposits by analyzing subsurface brines or other waters for the presence-of dissolved ions, in particular ions associated with the processes of seawater evaporation and brine diagenesis such as calcium, magnesium, potassium, bromine, and rubidium.

The search for bittern salts by geochemistry has heretofore been conducted by seeking evidence of high bromine content in the solid sodium chloride always associated with such deposits. One of the disadvantages of this method is that the salt section must be drilled or cored to obtain samples for anaiysis. Often wells drilled for hydrocarbons are bottomed above, or just when they enter salt sections and thus there is a dearth of the necessary geological information.

The present invention is directed to overcoming the problems encountered in geochemical prospecting as discussed above.

In general, the present invention is directed to a method of geochemical prospecting wherein information concerning the location of bittem salt deposits is derived by collecting samples of subterranean aqueous fluids from prospect areas and determining the concentration of dissolved ions which are affected by the processes of seawater evaporation and brine diagenesis. The presence of these dissolved ions in specific amounts or in specific ratios have been discovered to indicate that these subterranean waters have been in contact with, or are near, a bittem salt deposit since the reaction between bittern salts and itsassociated formation waters results in unique concentrations and ratios of certain ions common to both. In other words, the waters contain certain concentrations and ratios of ions that they could not contain had not bittem salts been precipitated from them. Specifically, increasing concentrations of bromine or rubidium, or decreasing ratios of bromine to potassium, (magnesium plus calcium) to rubidium or (magnesium plus calcium) to bromine indicate the direction, in both plan and profile, toward deposits.

Thus by measuring the concentration of ions associated with the process of seawater evaporation and brine diagenesisin fluid samples or cores containing such fluids it is possible to determine whether a particular underlying salt bed may contain bittern salts.

ln practicing this invention any suitable method of analysis may be employed, for example atomic absorption. The necessary samples may be obtained by swabbing gas and oil well bore holes, from drill-stem test fluids, as core fluids or any other convenient source of subterranean fluids. The samples to be utilized for a regression in the plan view of the formation will be obtained from a given stratigraphic zone. Samples utilized as profile indicators will be generally taken from a given localized area but from any stratigraphic level. A stratigraphic zone for the purposes of the instant invention is one consisting of a persistent stratum of some one kind of rock in which there is some porosity. 1

Generally, in accordance with this invention, the formation fluid samples are analyzed for the above mentioned ionvalues.

Having determinedthe specific concentrations of bromineand rubidium and the indicated ratios, the results of such analyses are plotted. This plot may take the form of an actual graphic representation of the data or any mathematical simulation of the same. When plotted, either in plan or in profile,

or in both, the regression analysis indicative of the location of bittem deposits will show a pattern of generally increasing 1 concentrations of bromine and/or rubidium or decreases in the specific ratios of Br/K, Mg'lRb or MgBr (wherein Mg equals the sum of magnesium and calcium ion values expressed as magnesium). A ratio of Br/K less than 0.17, Mg'IRb less than 3,000, or MglBr less than 14 each indicates underlying layers of bittem deposits. Each such ratio therefore serves also to indicate vertical direction to deposits. In plan view, two or more data points wherein the specific ratios are more than these values but wherein one or more of the ratios is closer to these values indicate horizontal directions to the deposits. Although the number of data points utilized is not critical s0 long as at least the two necessary to a directional vector are utilized in plan, preferred practice is tov seek a similar or coincident regression of two or-more of the indicator parameters.

Reliability is significantly improved, if the indicator parameter is based on'at least l fluid sample for every square miles included withinthe plan. As previously indicated, the samples utilized for developing a plan view should be taken from a given stratigraphic layer. In this manner a relatively highly definitive plan view of bittem locations is developed.

It is, of course true that there will be variations in the concentrations of the ions associated with the processes of seawater evaporation and brine diagenesis in the formation waters from differentlocalities due to the history of the waters and formations surrounding the waters, even in the absence of bittem salt deposits, however, larger variations will be found due to the presence of buried bittern deposits and as a rule the small natural variations are negligible as compared to the largervariations resulting from the presence of the deposits. Thus, in' the present invention, both the total amounts of ions as well as the trend, i.e., directional increases in the amount of ions in the water or the trend of certain ratios, are indicative of the presence of bitter'n salts.

To be significant iri'the practice of the instant invention, the data should contain concentrations of bromine and rubidium in excess of ten times their concentrations in seawater and variations in amounts of ions should exceed about 10 per cent of the same ion values from sample to the next adjacent sample included in the plot. Similarly, the variations in the ratio of bromine to potassium or magnesium to rubidium should vary significantly and at least one of these ratios should be less than the sameratio for seawater for a meaningful plot. Particularly, the ratio variation should exceed about 10 per cent of the same value from sample to the next adjacent sample to be included.

The following examples will illustrate how the instant invention may be utilized to locate bittern deposits.

EXAMPLE 1 I cation of a deposit.

TABLE I Sample ppm ppm Br Br/K 5-1 I 3,730 2,250 0.60 F 5-2 13,300 1,415 o."

5-3 13,800 I,I50 0.088 seawater 390 65 0.17

Exploration of the salt section'has shown that in the areas underlying S-2 and.S-3 sylvinite, a bittern salt, is present. In the area underlying S- 1 sylvinite is not present.

EXAMPLE 2 Table I1 lists the concentration of some ions and ratios associated with the processes of seawater evaporation and brine diagenesis in a vertical profile derived from formation waters from 10 different stratigraphic units in the same area. Formation 1 is nearest the surface, formation 2 is next nearest, etc., and Formation I0 is the deepest. As indicated in the table, salt occurs between formations 5 and 6, 6 and 7, and 9 and 10. The formation water data, compared with seawater, demonstrate that the trend of the ratios and their magnitudes are indicative of directions to bittern salL in vertical profile.

Exploration of the salt sections has shown that salt c contains sylvinite, a bittem salt. Salts a and b do not contain sylvinite.

EXAMPLE 3 Table 111 lists the concentration of some ions and ratios associated with the processes of seawater evaporation and brine diagenesis in formation waters from a single stratigraphic unit, Le, a carbonate unit which overlies and sand unit, which in turn overlies a salt unit. Again these data are compared to seawater. I

TABLE III 1 18,400 3,570 33 5.1 565 2 23,000 4,760 16 4.7 1,430 3 25.000 1.750 8 14.2 3,130 Seawater L300 65 0.12 20.0 10,800

Note: Mg is the sum of the magnesium in the brine and the calcium calculated u magnesium equivalent.

Since a great deal of magnesium is missing in areas 1 and 2 in comparison to area 3 and seawater, and since the rubidium and bromine concentration anomalies are higher in areas 1 and 2, the salt underlying these two areas may be inferred to contain the bittem salt camallite, KCl-MgCl,-6H,O.

The ion concentrations associated with the processes of seawater concentration and brine diagenesis illustrated above reveal the general nature of the results attainable by the practice of the present invention.

What is claimed is:

1. A method of exploring for bittem salt deposits which comprises: collecting samples of aqueous fluids from a given stratigraphic layer of subterrean formations in the prospect area; determining the concentrations and ratios in the aqueous fluids of at least one element combination selected from the group consisting of bromine to potassium, magnesium plus calcium to rubidium, and magnesium plus calcium to bromine; and developing plan view directional regressions of only ratios less than the equivalent ratio for seawater to produce a directional indication of the proximity of bittem salt deposits.

2. The method as in claim 1 wherein only ratios of bromine to potassium are plotted.

3. The method as in claim 1 wherein only ratios of magnesium plus calcium to rubidium are plotted.

4. The method as in claim 1 wherein only ratios of magnesium plus calcium to bromine are plotted.

5. The method of claim 2 wherein only ratios of bromine to potassium less than 0.17 are plotted.

6. The method of claim 3 wherein only ratios of magnesium plus calcium to rubidium less than 3,000 are plotted.

7. The method of claim 4 wherein only ratios of magnesium plus calcium to bromine less than 14 are plotted. 

2. The method as in claim 1 wherein only ratios of bromine to potassium are plotted.
 3. The method as in claim 1 wherein only ratios of magnesium plus calcium to rubidium are plotted.
 4. The method as in claim 1 wherein only ratios of magnesium plus calcium to bromine are plotted.
 5. The method of claim 2 wherein only ratios of bromine to potassium less than 0.17 are plotted.
 6. The method of claim 3 wherein only ratios of magnesium plus calcium to rubidium less than 3,000 are plotted.
 7. The method of claim 4 wherein only ratios of magnesium plus calcium to bromine less than 14 are plotted. 